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Transport and metabolic effects of α-aminoisobutyric acid in saccharomyces cerevisiae
Authors:Kyu Won Kim  Robert J Roon
Institution:University of Minnesota, Department of Biochemistry, 4-245 Millard Hall, 435 Delaware St. SE, Minneapolis, MN 55455 U.S.A.
Abstract:α-Aminoisobutyric acid is actively transported into yeast cells by the general amino acid transport system. The system exhibits a Km for α-aminoisobutyric acid of 270 μM, a Vmax of 24 nmol/min per mg cells (dry weight), and a pH optimum of 4.1–4.3. α-Aminoisobutyric acid is also transported by a minor system(s) with a Vmax of 1.7 nmol/min per mg cells. Transport occurs against a concentration gradient with the concentration ratio reaching over 1000:1 (in/out). The α-aminoisobutyric acid is not significantly metabolized or incorporated into protein after an 18 h incubation. α-Aminoisobutyric acid inhibits cell growth when a poor nitrogen source such as proline is provided but not with good nitrogen sources such as NH4+. During nitrogen starvation α-aminoisobutric acid strongly inhibits the synthesis of the nitrogen catabolite repression sensitive enzyme, asparaginase II. Studies with a mutant yeast strain (GDH-CR) suggest that α-aminoisobutyric acid inhibition of asparaginase II synthesis occurs because α-aminoisobutyric acid is an effective inhibitor of protein synthesis in nitrogen starved cells.
Keywords:α-Aminoisobutyric acid  Amino acid transport  (S  cerevisiae)
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